Many modern integrated circuits are fabricated using a design technology that is generally referred to as application specific integrated circuit technology, or ASIC technology. ASIC technology starts with a library of functional modules and standard processes, which are combined in a variety of different ways to produce unique integrated circuits. Thus, a customer can select from the functional modules offered by an ASIC fabricator to design an integrated circuit that is highly customized according to the needs of the customer's products. By using such technology, the cost of fabricating integrated circuits is dramatically reduced.
However, even though some costs can be dramatically reduced using such technology, other costs are not reduced to such a large extent. For example, one of the major costs of fabricating a unique integrated circuit design is the tooling cost associated with producing a mask or reticle set for the design. Although standard functional modules have been used in the design of the integrated circuit, these functional modules are combined into a unique reticle set in order to fabricate the new design. If a relatively large number of the integrated circuits are to be fabricated, these tooling costs can be spread across a great number of individual devices, and thus are relatively low on a per device basis. However, if only a relatively limited number of the integrated circuits are to be fabricated, then these tooling costs comprise a relatively greater economic load on each individual device so fabricated.
The cost of tooling, such as reticle sets, can be reduced by placing more than one integrated circuit design on each reticle of the reticle set. When this is done, then each design is fabricated on common substrates using the common reticle set. However, in order for this to work, certain conditions must be met. For example, it must be possible to appropriately singulate the different devices from one another when the fabrication process is complete. However, this is not too high a barrier, as there are many integrated circuit designs which meet this criteria.
Unfortunately, even though those criteria such as the ability to singulate may be met, other criteria might still prohibit two or more integrated circuit designs to be integrated into a common reticle set. For example, there may be processing differences between the two designs. Sometimes these processing differences are extreme, and thus the integration of the two different designs is not practical. However, other times the processing differences do not seem that great, yet a few seemingly small differences still prohibit the integration of the two or more designs into a single common reticle set.
For example, two different designs may be extremely similar, or virtually identical, in their processing requirements (not in their layout), except that one of the designs has a different conductive stack than the other design. For example, one of the designs may have a taller conductive stack, and the other design therefore has a shorter conductive stack. Although this may be the only difference in processing between the two different designs (remembering that the layout of the two designs may be vastly different), if has nevertheless been a sufficient difference to prohibit the integration of the two different designs into a common reticle set, because the taller stack design required more layers than the shorter stack design.
What is needed, therefore, is a system by which different integrated circuit designs which have different stack heights, but which otherwise have compatible process flows, can be integrated into a common reticle set and be fabricated on common substrates.